Adjustable Noise Attenuation Device for Use in Blow Through Air Handler/Furnace with Mixed Flow Blower Wheel

ABSTRACT

An HVAC system comprises an air flow path, a heat exchanger in the air flow path, a blower in the air flow path to move air through the heat exchanger, and at least one Helmholtz resonator in the air flow path. The Helmholtz resonator may be placed in numerous places throughout the air flow path. The Helmholtz resonator may be adjustable. The Helmholtz resonator further may be automatically adjustable. The automatic adjustment may be based on a characteristic of at least one of the blower or the air in the air flow path. Characteristics of air moving through the air flow path may include airspeed, absolute pressure, a pressure change through a portion of the HVAC system, or an audio characteristic. The automatic adjustment may be based on a feedback pressure or an electrical signal from a sensor. The system may have multiple Helmholtz resonators.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. 119(e) to U.S.Provisional Patent Application No. 62/013,693 filed on Jun. 18, 2014 byGroskreutz, et al. and entitled “Adjustable Noise Attenuation Device forUse in Blow Through Air Handler/Furnace with Mixed Flow Blower Wheel,”the disclosure of which is hereby incorporated by reference in itsentirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Heating, ventilation, and air conditioning systems (HVAC systems)generally comprise one or more heat exchangers generally referred to as“condensers” that may comprise a condenser coil, and may be associatedwith one or more compressors and one or more fan assemblies. Inoperation, a compressor may compress refrigerant and dischargesuperheated refrigerant (i.e., refrigerant at a temperature greater thana saturation temperature of the refrigerant) to the condenser coil. Asthe refrigerant passes through the condenser coil, a fan assembly may beconfigured to selectively force air into contact with the condensercoil. In response to the air contacting the condenser coil, heat may betransferred from the refrigerant to the air, thereby desuperheating therefrigerant and/or otherwise reducing a temperature of the refrigerant.In some cases, the temperature of the refrigerant within the condensercoil is reduced to a saturation temperature of the refrigerant.Continued removal of heat from the refrigerant at the saturationtemperature in combination with appropriately maintained pressure withinthe condenser coil may result in transforming some or all of the gaseousphase refrigerant to liquid phase refrigerant.

Refrigerant may generally exit the condenser coil in a liquid phaseand/or a gaseous and liquid mixed phase. The refrigerant may thereafterbe delivered from the condenser coil to a refrigerant expansion devicewhere the refrigerant pressure is reduced and after which, therefrigerant is selectively discharged into a so-called evaporator coilof the HVAC system that may provide a cooling function.

Likewise, an HVAC system may comprise a heat generating section. Theheat that is generated is used to heat air passing through the heatgenerating section. The heat may be generated via burning natural gas,burning coal, electric resistance wiring, and other methods that arewell known in the art.

Whether being used for heating or cooling, the core function of the HVACsystem is to move air either over the condensers or through the heatgenerating section, thereby altering the temperature of the air. The airis then distributed as desired. The air is moved using a blower of sometype.

SUMMARY

In an embodiment, an HVAC system comprises an air flow path, a blower inthe air flow path, a heat exchanger in the air flow path, and at leastone Helmholtz resonator operably connected to the air flow path. The atleast one Helmholtz resonator may be positioned in the air flow path ofthe blower. The HVAC system may also include a duct downstream orupstream of the heat exchanger. The duct may comprise at least one wall,and the at least one Helmholtz resonator may be operably connected tothe wall. The HVAC system may also include an air inlet orifice, and theat least one Helmholtz resonator may be operably connected to the airinlet orifice. The Helmholtz resonator may be adjustable.

In an embodiment, an HVAC system comprises an air flow path, a blower inthe air flow path, a heat exchanger in the air flow path, and at leastone Helmholtz resonator operably connected to the air flow path. The atleast one adjustable Helmholtz resonator is configured to adjustautomatically based on a characteristic of at least one of the blower oran air stream downstream of the blower. The at least one characteristicof the air moving through the HVAC system may comprise airspeed,absolute pressure, a pressure change through a portion of the HVACsystem, or an audio characteristic. The at least one adjustableHelmholtz resonator may be configured to adjust based on a feedbackpressure, an electrical signal from a sensor, and/or a speed of theblower. The air flow path further may comprise an inner fan housing, theinner fan housing may comprise at least one wall, and the Helmholtzresonator may be positioned in a wall of the inner fan housing.

In an embodiment, a method of reducing noise in an HVAC system comprisesmoving air through an air flow path in the HVAC system using a blower,generating a noise signal having acoustic energy in response to theblower moving the air, moving the air past a Helmholtz resonatoroperably connected to the blower, and dampening the acoustic energy ofthe noise signal with the Helmholtz resonator in response to moving theair past the Helmholtz resonator. The HVAC system comprises: the blowerand a heat exchanger. The method may also include adjusting theHelmholtz resonator in response to changes in at least one audiocharacteristic of the air. The adjusting may be performed automatically.The adjusting may be based on a feedback pressure, and the feedbackpressure may be a pressure differential between a pressure downstream ofthe blower and a pressure upstream of the blower. The adjusting may bebased on an electrical signal from a sensor associated with the blower.The adjusting may comprise changing a volume of the Helmholtz resonator.The adjusting may be based on a speed of the blower. The Helmholtzresonator may be built into a wall that is a portion of a duct ahead ofthe blower or in an air inlet orifice.

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and theadvantages thereof, reference is now made to the following briefdescription, taken in connection with the accompanying drawings anddetailed description:

FIG. 1 is a simplified schematic diagram of an HVAC system according toan embodiment of the disclosure;

FIG. 2 is a simplified schematic diagram of the air circulation paths ofthe HVAC system of FIG. 1;

FIG. 3 is a simplified schematic diagram of a portion of another HVACsystem according to an embodiment of the disclosure;

FIG. 4 is a simplified schematic diagram of a portion of another HVACsystem according to an embodiment of the disclosure;

FIG. 5 is a simplified schematic diagram of a portion of another HVACsystem according to an embodiment of the disclosure;

FIG. 6 is a simplified schematic diagram of a portion of another HVACsystem according to an embodiment of the disclosure.

DETAILED DESCRIPTION

In the drawings and description that follow, like parts are typicallymarked throughout the specification and drawings with the same referencenumerals, respectively. In addition, similar reference numerals mayrefer to similar components in different embodiments disclosed herein.The drawing figures are not necessarily to scale. Certain features ofthe invention may be shown exaggerated in scale or in somewhat schematicform and some details of conventional elements may not be shown in theinterest of clarity and conciseness. The present invention issusceptible to embodiments of different forms. Specific embodiments aredescribed in detail and are shown in the drawings, with theunderstanding that the present disclosure is not intended to limit theinvention to the embodiments illustrated and described herein. It is tobe fully recognized that the different teachings of the embodimentsdiscussed herein may be employed separately or in any suitablecombination to produce desired results.

One problem with some HVAC systems is that at certain constant speedsthey can create problematic noise that can be bothersome or irritatingto people exposed to that noise.

Referring now to FIG. 1, a simplified schematic diagram of an HVACsystem 100 is shown according to an embodiment of the disclosure. HVACsystem 100 generally comprises an indoor unit 102, an outdoor unit 104,and a system controller 106. The system controller 106 may generallycontrol operation of the indoor unit 102 and/or the outdoor unit 104. Asshown, the HVAC system 100 is a so-called heat pump system that may beselectively operated to implement one or more substantially closedthermodynamic refrigeration cycles to provide a cooling functionalityand/or a heating functionality.

Indoor unit 102 generally comprises an indoor heat exchanger 108, anindoor fan 110, and an indoor metering device 112. In an embodiment,indoor heat exchanger 108 is a plate fin heat exchanger configured toallow heat exchange between refrigerant carried within internal tubingof the indoor heat exchanger 108 and fluids that contact the indoor heatexchanger 108 but that are kept segregated from the refrigerant. Inother embodiments, indoor heat exchanger 108 may comprise a spine finheat exchanger, a microchannel heat exchanger, or any other suitabletype of heat exchanger.

In an embodiment, the indoor fan 110 is a centrifugal blower comprisinga blower housing, a blower impeller at least partially disposed withinthe blower housing, and a blower motor configured to selectively rotatethe blower impeller. In other embodiments, the indoor fan 110 maycomprise a mixed-flow fan and/or any other suitable type of fan. Theindoor fan 110 is configured as a modulating and/or variable speed fancapable of being operated at many speeds over one or more ranges ofspeeds. In other embodiments, the indoor fan 110 may be configured as amultiple speed fan capable of being operated at a plurality of operatingspeeds by selectively electrically powering different ones of multipleelectromagnetic windings of a motor of the indoor fan 110. In yet otherembodiments, the indoor fan 110 may be a single speed fan. Whileillustrated and described as a single indoor fan 110, a plurality offans may be present in any system, and each of the fans may be the sameor different than any of the other fans.

In an embodiment, the indoor metering device 112 is an electronicallycontrolled motor driven electronic expansion valve (EEV). In alternativeembodiments, the indoor metering device 112 may comprise a thermostaticexpansion valve, a capillary tube assembly, and/or any other suitablemetering device. The indoor metering device 112 may comprise and/or beassociated with a refrigerant check valve and/or refrigerant bypass foruse when a direction of refrigerant flow through the indoor meteringdevice 112 is such that the indoor metering device 112 is not intendedto meter or otherwise substantially restrict flow of the refrigerantthrough the indoor metering device 112.

Outdoor unit 104 generally comprises an outdoor heat exchanger 114, acompressor 116, an outdoor fan 118, an outdoor metering device 120, anda reversing valve 122. In an embodiment, outdoor heat exchanger 114 is aspine fin heat exchanger configured to allow heat exchange betweenrefrigerant carried within internal passages of the outdoor heatexchanger 114 and fluids that contact the outdoor heat exchanger 114 butthat are kept segregated from the refrigerant. In other embodiments,outdoor heat exchanger 114 may comprise a plate fin heat exchanger, amicrochannel heat exchanger, or any other suitable type of heatexchanger.

In an embodiment, the compressor 116 is a multiple speed scroll typecompressor configured to selectively pump refrigerant at a plurality ofmass flow rates. In alternative embodiments, the compressor 116 maycomprise a modulating compressor capable of operation over one or morespeed ranges, a reciprocating type compressor, a single speedcompressor, and/or any other suitable refrigerant compressor and/orrefrigerant pump.

In an embodiment, the outdoor fan 118 is an axial fan comprising a fanblade assembly and fan motor configured to selectively rotate the fanblade assembly. In other embodiments, the outdoor fan 118 may comprise amixed-flow fan, a centrifugal blower, and/or any other suitable type offan and/or blower. The outdoor fan 118 is configured as a modulatingand/or variable speed fan capable of being operated at many speeds overone or more ranges of speeds. In other embodiments, the outdoor fan 118may be configured as a multiple speed fan capable of being operated at aplurality of operating speeds by selectively electrically poweringdifferent ones of multiple electromagnetic windings of a motor of theoutdoor fan 118. In yet other embodiments, the outdoor fan 118 may be asingle speed fan. While illustrated and described as a single outdoorfan 118, a plurality of outdoor fans may be present in any system, andeach of the fans may be the same or different than any of the otherfans.

In an embodiment, the outdoor metering device 120 is a thermostaticexpansion valve. In alternative embodiments, the outdoor metering device120 may comprise an electronically controlled motor driven EEV similarto indoor metering device 112, a capillary tube assembly, and/or anyother suitable metering device. The outdoor metering device 120 maycomprise and/or be associated with a refrigerant check valve and/orrefrigerant bypass for use when a direction of refrigerant flow throughthe outdoor metering device 120 is such that the outdoor metering device120 is not intended to meter or otherwise substantially restrict flow ofthe refrigerant through the outdoor metering device 120.

In an embodiment, the reversing valve 122 is a so-called four-wayreversing valve. The reversing valve 122 may be selectively controlledto alter a flow path of refrigerant in the HVAC system 100 as describedin greater detail below. The reversing valve 122 may comprise anelectrical solenoid or other device configured to selectively move acomponent of the reversing valve 122 between operational positions.

In an embodiment, the system controller 106 may generally comprise atouchscreen interface for displaying information and for receiving userinputs. The system controller 106 may display information related to theoperation of the HVAC system 100 and may receive user inputs related tooperation of the HVAC system 100. However, the system controller 106 mayfurther be operable to display information and receive user inputstangentially and/or unrelated to operation of the HVAC system 100. Insome embodiments, the system controller 106 may not comprise a displayand may derive all information from inputs from remote sensors andremote configuration tools. In some embodiments, the system controller106 may comprise a temperature sensor and may further be configured tocontrol heating and/or cooling of zones associated with the HVAC system100. In some embodiments, the system controller 106 may be configured asa thermostat for controlling supply of conditioned air to zonesassociated with the HVAC system 100.

In some embodiments, the system controller 106 may also selectivelycommunicate with an indoor controller 124 of the indoor unit 102, withan outdoor controller 126 of the outdoor unit 104, and/or with othercomponents of the HVAC system 100. In some embodiments, the systemcontroller 106 may be configured for selective bidirectionalcommunication over a communication bus 128. In some embodiments,portions of the communication bus 128 may comprise a three-wireconnection suitable for communicating messages between the systemcontroller 106 and one or more of the HVAC system 100 componentsconfigured for interfacing with the communication bus 128. Stillfurther, the system controller 106 may be configured to selectivelycommunicate with HVAC system 100 components and/or any other device 130via a communication network 132. In some embodiments, the communicationnetwork 132 may comprise a telephone network, and the other device 130may comprise a telephone. In some embodiments, the communication network132 may comprise the Internet, and the other device 130 may comprise asmartphone and/or other Internet-enabled mobile telecommunicationdevice. In other embodiments, the communication network 132 may alsocomprise a remote server.

The indoor controller 124 may be carried by the indoor unit 102 and maybe configured to receive information inputs, transmit informationoutputs, and otherwise communicate with the system controller 106, theoutdoor controller 126, and/or any other device 130 via thecommunication bus 128 and/or any other suitable medium of communication.In some embodiments, the indoor controller 124 may be configured tocommunicate with an indoor personality module 134 that may compriseinformation related to the identification and/or operation of the indoorunit 102. In some embodiments, the indoor controller 124 may beconfigured to receive information related to a speed of the indoor fan110, transmit a control output to an electric heat relay, transmitinformation regarding an indoor fan 110 volumetric flow-rate,communicate with and/or otherwise affect control over an air cleaner136, and communicate with an indoor EEV controller 138. In someembodiments, the indoor controller 124 may be configured to communicatewith an indoor fan controller 142 and/or otherwise affect control overoperation of the indoor fan 110. In some embodiments, the indoorpersonality module 134 may comprise information related to theidentification and/or operation of the indoor unit 102 and/or a positionof the outdoor metering device 120.

In some embodiments, the indoor EEV controller 138 may be configured toreceive information regarding temperatures and/or pressures of therefrigerant in the indoor unit 102. More specifically, the indoor EEVcontroller 138 may be configured to receive information regardingtemperatures and pressures of refrigerant entering, exiting, and/orwithin the indoor heat exchanger 108. Further, the indoor EEV controller138 may be configured to communicate with the indoor metering device 112and/or otherwise affect control over the indoor metering device 112. Theindoor EEV controller 138 may also be configured to communicate with theoutdoor metering device 120 and/or otherwise affect control over theoutdoor metering device 120.

The outdoor controller 126 may be carried by the outdoor unit 104 andmay be configured to receive information inputs, transmit informationoutputs, and otherwise communicate with the system controller 106, theindoor controller 124, and/or any other device via the communication bus128 and/or any other suitable medium of communication. In someembodiments, the outdoor controller 126 may be configured to communicatewith an outdoor personality module 140 that may comprise informationrelated to the identification and/or operation of the outdoor unit 104.In some embodiments, the outdoor controller 126 may be configured toreceive information related to an ambient temperature associated withthe outdoor unit 104, information related to a temperature of theoutdoor heat exchanger 114, and/or information related to refrigeranttemperatures and/or pressures of refrigerant entering, exiting, and/orwithin the outdoor heat exchanger 114 and/or the compressor 116. In someembodiments, the outdoor controller 126 may be configured to transmitinformation related to monitoring, communicating with, and/or otherwiseaffecting control over the outdoor fan 118, a compressor sump heater, asolenoid of the reversing valve 122, a relay associated with adjustingand/or monitoring a refrigerant charge of the HVAC system 100, aposition of the indoor metering device 112, and/or a position of theoutdoor metering device 120. The outdoor controller 126 may further beconfigured to communicate with a compressor drive controller 144 that isconfigured to electrically power and/or control the compressor 116.

The HVAC system 100 is shown configured for operating in a so-calledcooling mode in which heat is absorbed by refrigerant at the indoor heatexchanger 108 and heat is rejected from the refrigerant at the outdoorheat exchanger 114. In some embodiments, the compressor 116 may beoperated to compress refrigerant and pump the relatively hightemperature and high pressure compressed refrigerant from the compressor116 to the outdoor heat exchanger 114 through the reversing valve 122and to the outdoor heat exchanger 114. As the refrigerant is passedthrough the outdoor heat exchanger 114, the outdoor fan 118 may beoperated to move air into contact with the outdoor heat exchanger 114,thereby transferring heat from the refrigerant to the air surroundingthe outdoor heat exchanger 114. The refrigerant may primarily compriseliquid phase refrigerant and the refrigerant may flow from the outdoorheat exchanger 114 to the indoor metering device 112 through and/oraround the outdoor metering device 120 which does not substantiallyimpede flow of the refrigerant in the cooling mode. The indoor meteringdevice 112 may meter passage of the refrigerant through the indoormetering device 112 so that the refrigerant downstream of the indoormetering device 112 is at a lower pressure than the refrigerant upstreamof the indoor metering device 112. The pressure differential across theindoor metering device 112 allows the refrigerant downstream of theindoor metering device 112 to expand and/or at least partially convertto a two-phase (vapor and gas) mixture. The two phase refrigerant mayenter the indoor heat exchanger 108. As the refrigerant is passedthrough the indoor heat exchanger 108, the indoor fan 110 may beoperated to move air into contact with the indoor heat exchanger 108,thereby transferring heat to the refrigerant from the air surroundingthe indoor heat exchanger 108, and causing evaporation of the liquidportion of the two phase mixture. The refrigerant may thereafterre-enter the compressor 116 after passing through the reversing valve122.

To operate the HVAC system 100 in the so-called heating mode, thereversing valve 122 may be controlled to alter the flow path of therefrigerant, the indoor metering device 112 may be disabled and/orbypassed, and the outdoor metering device 120 may be enabled. In theheating mode, refrigerant may flow from the compressor 116 to the indoorheat exchanger 108 through the reversing valve 122, the refrigerant maybe substantially unaffected by the indoor metering device 112, therefrigerant may experience a pressure differential across the outdoormetering device 120, the refrigerant may pass through the outdoor heatexchanger 114, and the refrigerant may reenter the compressor 116 afterpassing through the reversing valve 122. Most generally, operation ofthe HVAC system 100 in the heating mode reverses the roles of the indoorheat exchanger 108 and the outdoor heat exchanger 114 as compared totheir operation in the cooling mode.

Referring now to FIG. 2, a simplified schematic diagram of the aircirculation paths for a structure 200 conditioned by two HVAC systems100 is shown. In this embodiment, the structure 200 is conceptualized ascomprising a lower floor 202 and an upper floor 204. The lower floor 202comprises zones 206, 208, and 210 while the upper floor 204 compriseszones 212, 214, and 216. The HVAC system 100 associated with the lowerfloor 202 is configured to circulate and/or condition air of lower zones206, 208, and 210 while the HVAC system 100 associated with the upperfloor 204 is configured to circulate and/or condition air of upper zones212, 214, and 216.

In addition to the components of HVAC system 100 described above, inthis embodiment, each HVAC system 100 further comprises a ventilator146, a prefilter 148, a humidifier 150, and a bypass duct 152. Theventilator 146 may be operated to selectively exhaust circulating air tothe environment and/or introduce environmental air into the circulatingair. The prefilter 148 may generally comprise a filter media selected tocatch and/or retain relatively large particulate matter prior to airexiting the prefilter 148 and entering the air cleaner 136. Thehumidifier 150 may be operated to adjust a humidity of the circulatingair. The bypass duct 152 may be utilized to regulate air pressureswithin the ducts that form the circulating air flow paths. In someembodiments, air flow through each bypass duct 152 may be selectivelyregulated by each respective bypass damper 154, while air flow deliveredto each of zones 206, 208, 210, 212, 214, and 216 through air supplyducts 234, 236, 238, 240, 242, and 244, respectively, may be selectivelyregulated by corresponding optional zone dampers 156. In someembodiments, return air flow to lower zone return plenum 218 may flowthrough return ducts 220, 222, and 224 and may be selectively regulatedby return dampers 246, 248, and 250, respectively. In some embodiments,return air flow to upper zone return plenum 226 may flow through returnducts 228, 230, and 232 and may be selectively regulated by returndampers 252, 254, and 256, respectively. In other embodiments, returnair through return ducts 220, 222, 224, 228, 230, and 232 may beselectively aided by controllable, variable speed return fans 258, 260,262, 264, 266, and 268, respectively.

Each HVAC system 100 may also further comprise a zone thermostat 158 anda zone sensor 160. In some embodiments, a zone thermostat 158 maycommunicate with the system controller 106 and may allow a user tocontrol a temperature, humidity, and/or other environmental setting forthe zone in which the zone thermostat 158 is located. Further, the zonethermostat 158 may communicate with the system controller 106 to providetemperature, humidity, and/or other environmental feedback regarding thezone in which the zone thermostat 158 is located. In some embodiments, azone sensor 160 may also communicate with the system controller 106 toprovide temperature, humidity, and/or other environmental feedbackregarding the zone in which the zone sensor 160 is located. In addition,in some embodiments, the system controller 106 may also monitortemperature, humidity, and/or other environmental settings for the zonein which the system controller 106 is located.

In some embodiments, the system controllers 106 may be configured forbidirectional communication with each other and may further beconfigured so that a user may, using any of the system controllers 106,monitor and/or control any of the HVAC system 100 components regardlessof which zones the components may be associated with. Further, eachsystem controller 106, each zone thermostat 158, and each zone sensor160 may comprise a humidity sensor and/or a temperature sensor. As such,it will be appreciated that structure 200 is equipped with a pluralityof humidity sensors and/or a plurality of temperature sensors in aplurality of different locations. Accordingly, each system controller106, zone thermostat 158, and zone sensor 160 may comprise a wired orwireless connection depending on the configuration of the HVAC system100. In some embodiments, a user may effectively select which of theplurality of humidity sensors and/or plurality of temperature sensors isused to control operation of one or more of the HVAC systems 100.

While HVAC systems 100 are shown as a so-called split system comprisingan indoor unit 102 located separately from the outdoor unit 104,alternative embodiments of an HVAC system 100 may comprise a so-calledpackage system in which one or more of the components of the indoor unit102 and one or more of the components of the outdoor unit 104 arecarried together in a common housing or package. The HVAC system 100 isshown as a so-called ducted system where the indoor unit 102 is remotelylocated from the conditioned zones, thereby requiring air ducts 234,236, 238, 240, 242, and 244 to route the circulating air.

HVAC systems are constantly being improved in various ways. Oneundesirable characteristic of HVAC systems is that they can producenoise, sometimes at levels that are not enjoyable to people nearby.Helmholtz resonators can be used in an HVAC system to reduce theacoustic energy of certain frequencies of sound coming from the system.

Referring now to FIG. 3, a simplified schematic diagram of a portion 300of an HVAC system is shown according to an embodiment of the disclosure.The portion 300 can be part of either an indoor or outdoor unit, thoughthe indoor unit is more likely to have noise issues. Included in portion300 is a section of upstream ductwork 302, an air intake orifice 304, aheat exchanger 306, a blower 308, a downstream section of ductwork 310and a Helmholtz resonator 312. Elements 302, 304, 306, 308 and 310together comprise an air flow path 318. As stated above, a complete HVACsystem would also include numerous other components, such ascontrollers, filters, etc.

The moving of air along the air flow path 318 is accomplished primarilyby the blower 308. The air is moved into the upstream ductwork 302,through the air intake orifice 304, through the blower 308, through theheat exchanger 306, and then out through the downstream ductwork 310.

While in FIG. 3 the blower 308 is shown being proximate the heatexchanger 306, the blower could be placed in other locations relative toor within the air flow path 318, so long as the blower 308 is able tomove air through the air flow path 318. For instance, the blower couldbe located before or in the upstream ductwork 302, in or after thedownstream ductwork 310, or other locations that would move air throughthe air flow path 318. A preferred system may have more than one blower308 moving air through the air flow path 318. Further, multiple blowerscould be located in different locations. The blower 308 could be a moretraditional forward curve blower, or it preferably could be a mixed flowtype blower as described in more detail herein. Mixed flow type blowersoffer significant efficiency benefits compared to forward curve blowers,but they also can produce noise in specific frequencies. This noise maybe unpleasant to some people who are exposed to it.

The blower 308 further comprises blades 314 set within an inner fanhousing 316. To optimize performance of the blower 308, the blades 314are set very close to the surface of the inner fan housing 316. By beingset very close, the blades 314 create a chopping effect on the airmoving along the air flow path 318, and thereby, a certain frequency ofsound, which may be related to the rotational speed of the blades 314.

The Helmholtz resonator 312 is shown in the downstream ductwork 310. TheHelmholtz resonator 312 can also be in other locations in the airstream,such as in the upstream ductwork, in the air inlet orifice, or in theinner fan housing. The Helmholtz resonator 312 can be of various formsand configurations as are well known in the art, such as a tube, aperforated honeycomb sheet, or other structure. The Helmholtz resonator312 can be a separate unit that is installed into the system, or it maybe comprised partially or completely by various surfaces already presentin the system, such as walls, etc., thereby reducing the number of partsneeded and possibly the cost of the resonator. Multiple Helmholtzresonators can be used in the system.

A Helmholtz resonator (or Helmholtz oscillator, as it is also known) isa container of gas (usually air) with an open hole (or neck or port). Avolume of air in and near the open hole vibrates because of the‘springiness’ of the air inside. A common example is an empty bottle. Toillustrate how it works, air moving across the top of the bottle causesthe air inside to vibrate. The vibration is due to the ‘springiness’ ofair. When compressed, the pressure of the air in the bottle increasesand the air tends to expand back to its original volume. Consider a‘lump’ of air at the neck of a bottle. The passing air jet can forcethis lump of air a little way down the neck, thereby compressing the airinside. That pressure now drives the ‘lump’ of air out but, when it getsto its original position, its momentum takes it outside the body a smalldistance. This rarifies the air inside the body, which then sucks the‘lump’ of air back in. It can thus vibrate like a mass on a spring. Thejet of air passing over the opening is capable of deflecting alternatelyinto the bottle and outside, which provides the power to keep theoscillation going.

Helmholtz resonators make a somewhat restrictive specific frequency ofsound, depending on the volume of the resonator, the length of the neck,and the area of the opening. The equation for calculating the resultantfrequency is

$f = {\frac{v}{\pi} \times \sqrt{\frac{A}{VL}}}$

where f is the resultant frequency, v is the velocity of sound, V is thevolume of the resonator, A is the area of the opening, and L is thelength of the neck. Thereby, one can change the frequency being issuedfrom it by varying any of the variables V, A or L.

A Helmholtz resonator can be used to absorb and/or cancel a particularfrequency. This is, if the Helmholtz resonator has a frequency set atthe problematic frequency one wishes to dampen, the acoustic energy ofthe frequency in the passing air can stimulate resonance in theHelmholtz resonator, thereby taking away energy at the desired frequencyfrom the acoustic energy in the passing air. Hence, it may be beneficialto have a Helmholtz resonator present in the air flow path 318 to atleast partially dampen the acoustic energy of a problematic frequencycaused by the fan blades 314 interacting with the inner housing surface316.

If the blower operates only at one speed, then it is a relatively simpleprocess to calculate the problematic frequency and design a Helmholtzresonator to cancel or reduce the energy of the problematic frequency.If the blower operates at various speeds, it may be that differentproblematic frequencies arise at different blower speeds. In such asituation, it may be desirable to use an adjustable Helmholtz resonator.That is, and referring again to FIG. 3, the blower 308 can use avariable speed motor. Thereby, the blower 308 may generate differentfrequencies of sound in the airflow at different speeds, at least someof those differing frequencies being problematic to people proximate theHVAC system. It may be that only one frequency is problematic, and hencea fixed Helmholtz resonator is sufficient. But if there are multiplepossible problematic frequencies, a variable Helmholtz resonator can beincluded in the air stream.

While Helmholtz resonators can be tuned numerous ways, specifically byvarying one or more of the variables V, A and L, typically the easiestand simplest variable to alter would be the volume. Referring now toFIG. 4, a simplified schematic diagram of a portion 400 of an HVACsystem is shown according to an embodiment of the disclosure. Includedin portion 400 is a section of upstream ductwork 402, an air intakeorifice 404, a heat exchanger 406, a blower 408, a downstream section ofductwork 410, a Helmholtz resonator 412, and a controller 414. Elements402, 404, 406, 408 and 410 together comprise an air flow path 420. Thecontroller 414 controls both the blower 408 and the Helmholtz resonator412. The Helmholtz resonator 412 comprises a tube with a movable bottomsection 416 to allow the volume of the resonator to be varied. Whileshown in this particular configuration, one can readily see that thereare any number of ways to vary the volume V.

Through testing prior to installation of the unit, the potentialproblematic frequencies can be correlated with the various speeds of theblower 408, and the appropriate volume V can be calculated to yield thedesired result. In operation, the controller 414, which may already bycontrolling the speed of blower 408, may also control the volume V ofthe Helmholtz resonator 412 to optimally reduce the acoustic energy ofvarious problematic frequencies in the air flow path 420.

The volume V of the Helmholtz resonator can also be dynamically and/orselectively adjusted during use. Referring now to FIG. 5, in anotherembodiment, a simplified schematic diagram of a portion 500 of an HVACsystem is shown according to an embodiment of the disclosure. Includedin portion 500 is a section of upstream ductwork 502, an air intakeorifice 504, a heat exchanger 506, a blower 508, a downstream section ofductwork 510, a Helmholtz resonator 512, a controller 514 and a sensor516. Elements 502, 504, 506, 508 and 510 together comprise an air flowpath 520. The sensor 516 is able to sense a characteristic of the air inthe air flow path 520. That characteristic could be an actualmeasurement of frequencies, or some other characteristic that wouldallow one to determine what frequencies are present in the air flow path520. The controller 514 is operably connected to the Helmholtz resonator512, and able to control the volume V. The Helmholtz resonator 512comprises a tube with a movable bottom section 518 to allow the volume Vof the resonator to be varied. The controller 514 is able to control theposition of the movable bottom section 518, and hence the volume V. Thesensor 516 is likewise connected to the controller 514. The controller514 then uses the data provided by the sensor 516 to determine apreferable position for the movable bottom section 518, and moved it tothat position accordingly.

In the alternative, the controller 514 could be combined with either theHelmholtz resonator 512, or the sensor 516. Or, the controller 514 couldbe part of the main controller that controls the fan, not shown.

The portion 500 may include more than one sensor, to measure, e.g.,pressure at various points in the air flow path 520. The collectedinformation may possibly be useful as an alternative way to estimate thefrequency of sounds in the air flow path 520.

While the Helmholtz resonator 512 is shown in this particularconfiguration, one can readily see that there are any number of ways tovary the volume V. Likewise, one could also choose to vary the length ofthe neck L, or the area of the opening A.

It is also possible to allow manual adjustment of the Helmholtzresonator 512. This would be accomplished by connecting the controller514 to a dial (not shown) that would be accessible to a person listeningto the HVAC system. Thereby, the fine tuning could be by ear.

Referring now to FIG. 6, in another embodiment, a simplified schematicdiagram of a portion 600 of an HVAC system is shown according to anembodiment of the disclosure. Included in portion 600 is a section ofupstream ductwork 602, an air intake orifice 604, a heat exchanger 606,a blower 608, a downstream section of ductwork 610, a Helmholtzresonator 612, an air inlet filter 614 and a pitot tube 616. Elements602, 604, 606, 608, 610 and 614 together comprise an air flow path 620.Air entering the air flow path 620 experiences a pressure drop acrossthe air inlet filter 614. The air also experiences a pressure riseacross the blower 608. With moving air the total air pressure(static+dynamic pressure) is higher than the static air pressure. Theinlet to the Helmholtz resonator 612 “sees” static air pressure at theair intake orifice 604 (low pressure area). A pitot tube 616 or similardevice may be oriented to “see” total air pressure at the blowerdischarge (high pressure area). The pressure differential between thestatic air inlet pressure and the total air discharge pressure may beutilized to actuate a device that changes the volume of the Helmholtzresonator. For example, a piston 618 inside the Helmholtz resonator 612may move based on the pressure differential experienced. The portion 600may also include a controller, not shown, that may use the pressuredifferential to determine a setting for the piston 618 and move piston618 accordingly. The pressure differential may also be used to activatea device that changes other features of the Helmholtz resonator in orderto change the operating frequency of said device.

At least one embodiment is disclosed and variations, combinations,and/or modifications of the embodiment(s) and/or features of theembodiment(s) made by a person having ordinary skill in the art arewithin the scope of the disclosure. Alternative embodiments that resultfrom combining, integrating, and/or omitting features of theembodiment(s) are also within the scope of the disclosure. Use ofbroader terms such as comprises, includes, and having should beunderstood to provide support for narrower terms such as consisting of,consisting essentially of, and comprised substantially of. Accordingly,the scope of protection is not limited by the description set out abovebut is defined by the claims that follow, that scope including allequivalents of the subject matter of the claims. Each and every claim isincorporated as further disclosure into the specification and the claimsare embodiment(s) of the present invention.

What is claimed is:
 1. An HVAC system comprising: an air flow path; ablower in the air flow path; a heat exchanger in the air flow path; andat least one Helmholtz resonator, operably connected to the air flowpath.
 2. The HVAC system of claim 1, wherein the at least one Helmholtzresonator is positioned in the air flow path of the blower.
 3. The HVACsystem of claim 1, further comprising a duct downstream or upstream ofthe heat exchanger, the duct comprising at least one wall, the at leastone Helmholtz resonator operably connected to the wall.
 4. The HVACsystem of claim 1, further comprising an air inlet orifice, wherein theat least one Helmholtz resonator is operably connected to the air inletorifice.
 5. The HVAC system of claim 1, wherein the Helmholtz resonatoris adjustable.
 6. An HVAC system comprising: an air flow path; a blowerin the air flow path; a heat exchanger in the air flow path; and atleast one Helmholtz resonator, operably connected to the air flow path,wherein the at least one adjustable Helmholtz resonator is configured toadjust automatically based on a characteristic of at least one of theblower or an air stream downstream of the blower.
 7. The HVAC system ofclaim 6, wherein the at least one characteristic of the air movingthrough the HVAC system comprises airspeed, absolute pressure, apressure change through a portion of the HVAC system, or an audiocharacteristic.
 8. The HVAC system of claim 6, wherein the at least oneadjustable Helmholtz resonator is configured to adjust based on afeedback pressure.
 9. The HVAC system of claim 6, wherein the at leastone adjustable Helmholtz resonator is configured to adjust based on anelectrical signal from a sensor.
 10. The HVAC system of claim 6, whereinthe at least one adjustable Helmholtz resonator is configured to adjustbased on a speed of the blower.
 11. The HVAC system of claim 6, whereinthe air flow path further comprises an inner fan housing, the inner fanhousing comprising at least one wall, wherein the Helmholtz resonator ispositioned in a wall of the inner fan housing.
 12. A method of reducingnoise in an HVAC system, the method comprising: moving air through anair flow path in the HVAC system using a blower, wherein the HVAC systemcomprises: the blower and a heat exchanger; generating a noise signalhaving acoustic energy in response to the blower moving the air; movingthe air past a Helmholtz resonator operably connected to the blower; anddampening the acoustic energy of the noise signal with the Helmholtzresonator in response to moving the air past the Helmholtz resonator.13. The method of claim 12, further comprising adjusting the Helmholtzresonator in response to changes in at least one audio characteristic ofthe air.
 14. The method of claim 13, wherein the step of adjusting isperformed automatically.
 15. The method of claim 13, wherein the step ofadjusting is based on a feedback pressure.
 16. The method of claim 15,wherein the feedback pressure is a pressure differential between apressure downstream of the blower and a pressure upstream of the blower.17. The method of claim 13, wherein the step of adjusting is based on anelectrical signal from a sensor associated with the blower.
 18. Themethod of claim 13, wherein the step of adjusting comprises changing avolume of the Helmholtz resonator.
 19. The method of claim 12, whereinthe step of adjusting is based on a speed of the blower.
 20. The methodof claim 12, wherein the Helmholtz resonator is built into a wall thatis a portion of a duct ahead of the blower or in an air inlet orifice.